The present invention relates to a dielectric duplexer of a type to be used for a mobile telecommunication device such as a car telephone set or a portable telephone set.
FIG. 1 of the accompanying drawings illustrates a typical conventional dielectric duplexer of the type under consideration. The dielectric duplexer D comprises as essential components thereof a dielectric ceramic block B, resonators t1 through t3 and r1 through r3 formed in the dielectric ceramic block B by cutting through holes through the dielectric ceramic block B sequentially along a direction and covering the inner peripheral surfaces of the through holes with respective internal conductors. The resonators are divided into a group of resonators t1 through t3 located near a lateral side of the dielectric ceramic block B and operating as a transmitting section T and another group of resonators r1 through r3 located near the opposite lateral side of the dielectric ceramic block B and operating as a receiving section R. An external conductor is provided for covering the outer peripheral surface of the dielectric ceramic block B except an open-circuit end surface intended for exposing the through holes to the outside. An input/output pad Pt is arranged on the bottom surface of the dielectric ceramic block B to be brought into contact with a printed circuit board when being assembled, and electrically isolated from the external conductor but capacitively coupled to the outermost resonator t1. Another input/output pad Pr is arranged also on the bottom surface of the dielectric ceramic block B and electrically isolated from the external conductor but capacitively coupled to the outermost resonator r3. Further, an antenna terminal pad Pa is arranged also on the bottom surface of the dielectric ceramic block B and electrically isolated from the external conductor. A variety of dielectric duplexers of the above described type have been proposed.
The dielectric duplexer D of FIG. 1 additionally comprises a wave-dividing resonator S arranged between the transmitting section T including the resonators t1 through t3 and the receiving section R including the resonators r1 through r3 at a position corresponding to the antenna terminal pad Pa arranged on the bottom surface of the dielectric ceramic block B.
FIG. 2 is an equivalent circuit diagram of the dielectric duplexer D of FIG. 1.
With this arrangement, the wave-dividing resonator S is located at the middle of the dielectric ceramic block B and hence the latter is required to have a large width. This means that a completed dielectric duplexer is of large size.
It is, therefore, an object of the present invention to provide a dielectric duplexer having a reduced width to eliminate the above identified problem.